Thermal recovery of oil



ABSTRACT OF THE DISCLOSURE Improved thermal in situ recovery of hydrocarbons is effected by contacting an oil-bearing stratum with a hot gas, such as steam or air, under oil cracking conditions and providing in the cracking zone injected readily dehydrogenatable hydrocarbon material, such as aromaticnaphthenic compounds, thereby reducing coke formation.

This invention relates to an improved process for the thermal recovery of oil involving high temperature cracking of the in-place oil.

It is conventional to produce oil from an oil-bearing stratum by thermal drive utilizing steam or hot combustion gas, generally produced in situ, to heat and displace oil from the stratum into one or more production wells. In either a high temperature steam drive or an in situ combustion drive, coke is produced in the stratum and becomes substantially unrecoverable in the process. Hence, it is desirable to reduce in situ coke formation as much as possible to improve efficiency of recovery.

This invention is concerned with the thermal recovery of oil with reduced coke formation.

Accordingly, it is an object of the invention to provide 'an improved process for the thermal recovery of oil.

Another object is to provide an improved thermal recovery process which suppresses and minimizes in situ coke formaton as applied to an oil-bearing stratum. A further object is to improve oil recovery in an in situ thermal drive process in an oil-bearing stratum. Other objects of the invention will become apparent to one skilled in the art upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises simultaneously contacting an oil-bearing stratum with a hot gas at cracking temperatures in a cracking zone and providing in said zone during cracking a readily dehydrogenatable hydrocarbon material under the conditions in the cracking zone so as to depress coke formation, and recovering the hydrocarbons produced by the cracking and thermal drive. The cracking zone is established either by injecting high temperature steam or by igniting the oil in the stratum and burning same with injected oxygen-containing, combustion-supporting gas, such as air. The injection of steam at temperatures in the range of about 600-850 E. into an oil-bearing stratum establishes a cracking zone which normally produces a substantial amount of coke and leaves this coke in the stratum. In situ combustion is' readily effected at cracking temperatures in the range of about 600 or 650? F. to 1200" F. and even higher such as up to 1600 F. Generally, the temperature in an in situ combustion drive is controlled in the range of about 750 to 1000 F.

The thermal drive process may be effected around a single well in known manner. One procedure when utilizing steam as the heating medium comprises injecting steam into the stratum thru an injection well while maintaining any surrounding Wells in the stratum shut in so that substantial steam pressure is built up in the stratum surrounding the injection well. After a substantial soaking period, the pressure on the injection well is released so as to allow the pressure in the stratum to force fluids into the injection well and these fluids include hydrocar- United States Patent O pounds are particularly effective. Compounds which are 3,342,260 Patented Sept. 19, 1967 bons expelled from the stratum, a portion of which is cracked by the high temperature steam. It is also feasible to pack off a section of the injection borehole and inject steam thru the stratum around the packed off section so as to recover produced hydrocarbons thru a well conduit separate from the steam injection conduit.

It is also feasible to conduct an in situ combustion drive thru a stratum around a single well in the aforesaid manner by packing off a section of the bore hole within the stratum being produced.

In strata which have adequate permeability, production generally comprises injecting the selected gas thru an in jection well and producing displaced oil and cracked products thru one or more offset production wells. One technique comprises injecting steam or combustion supporting gas thru a central well of a conventional spot pattern and producing hydrocarbons from the thermal drive from the surrounding ring wells. Another technique comprises injecting the selected gas thru a line of injection wells and producing the expelled hydrocarbons from lines of production wells on either side of the line of injection wells as in a conventional in-line drive.

In each of the foregoing techniques, coking is suppressed and reduced by providing in the cracking zone a readily dehydrogenatable hydrocarbon material under the conditions in the cracking zone. The hydrocarbon materials which have been found suitable for supplying hydrogen lin, but other compounds such a Decalin or hydrogenated naphthenes, anthracenes, and other condensed ring compounds and their homologs are useful and effective. The dihydio-, tetrahydro-, andhexahydroforms of these comnormally solid are readily vaporizable into the injected gas when heated to an elevated temperature. All of the compounds are readily dispersable in gaseous form in the injected stream. When utilizing in situ combustion to establish the cracking zone in the stratum by igniting inplace oil and feeding air or other combustion-supporting gas thereto, the hydrogen transfer material may be injected .with the air when such is feasible, depending upon the volatility of the material. When utilizing hydrocarbon material as the hydrogen transfer agent which is not readily "dispersablein the injected air, the hydrocarbon material may be dissolved in a hydrocarbon solvent such as'pentane, gasoline, kerosene, gas oil, or any hydrocarbon fraction recovered from the stratum which dissolves the hydrocarbonmaterial, and the solution may then be in jected into the stratum with the injected air in the form of an aerosol or the solution may be injected into the ,stratum prior to'the initiation of combustion therein so that as the combusion zone is driven thru the stratum, the

. hydrogen transfer agent is readily available in the cracking zone for suppressing coke formation.

In in situ combustion using direct drive of the combustion zone from an injection Well to a production well, the coke suppressing material is preferably injected into the formation prior to the initiation of combustion. In this manner the injected material is in-place when the cracking of the in-place oil begins and functions as soon as the reaction temperature is reached.

In counterflow combustion involving igniting a stratum around a production well and injecting air to the ignited zone thru the stratum from an offset injection well, injection of the hydrogen transfer material can be prior to actual ignition or it may be injected as an aerosol together with the combustion-supporting gas thru the injection well either continuously or intermittently. It is also feasible to inject the material thru a separate well (or thru the production well) into the vicinity of the combustion zone where the cracking occurs, prior to initiation of the thermal drive.

When using high temperature steam injection, the hydrocarbon material supplying the hydrogen is readily injected with the steam and this method is preferred. However, it is feasible to inject the material immediately following the steam injection during the quiescent soaking phase of the production cycle when utilizing the so-called buff and puff method. In this manner the hydrogen transfer material is available during the hydrocracking taking place in the stratum.

It is believed that the water-gas reaction which occurs in thermal drive recovery furnishes additional hydrogen to the hydrogen donor or hydrogen transfer material. The exact mechanism of the coke suppression is not completely understood but it has been found that most of the injected hydrocarbon material is readily recoverable from the production well efiluent by conventional methods and can be recycled during operation or reused in further thermal drive operation. The recovery and recycle of these hydrocarbon materials contributes substantially to the economy of the process.

When injecting the hydrocarbon material which is to suppress coke formation, prior to the thermal drive, the amount to be injected depends upon the character of the in-place oil being produced. Generally, an amount in the range of 0.05 to 1.0 pore volumes is adequate for obtaining the desired result (coke suppression). When injecting the hydrocarbon material with the injected steam or injected air, a concentration thereof in the range of 0.01 to 1.5 weight percent suffices.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

1. In a process for recovering oil from an oil-bearing stratum comprising igniting a zone of said stratum around a well therein and burning a portion of the in-place oil by feeding oxygen-containing gas to the ignited zone so as to burn a portion of the in-place oil, crack another portion, and produce hydrocarbons thru a well therein, the improvement comprising injecting into said stratum a hydrocarbon material comprising at least one aromaticnaphthenic compound readily dehydrogenatable under the conditions in the burning zone and providing said material within said burning zone so as to supply hydrogen therein and depress coke formation.

2. The process of claim 1 wherein said hydrocarbon material comprises Tetralin.

3. The process of claim 1 wherein said hydrocarbon material comprises Decalin.

4. A process for recovering oil from an oil-bearing stratum penetrated by an injection well and a production Well which comprises the steps of (1) establishing a combustion zone in said stratum ad jacent one of said wells;

(2) feeding oxygen-containing, combustion-supporting gas into said zone so as to burn a portion of the inplace oil, crack another portion to lighter hydrocarbons, and produce coke; (3) supplying a hydrocarbon material comprising at least one aromatic-naphthenic compound in said 5 combustion zone during combustion which dehydrogenates under the conditions therein so as to provide hydrogen for hydrogenation of cracked products thereby suppressing coke formation in the combustion zone; and

(4) recovering hydrocarbons produced by said combustion thru said production well.

5. The process of claim 4 wherein said hydrocarbon material comprises Tetralin.

6. In a process for recovering oil from an oil-bearing stratum comprising contacting said oil in said stratum with a hot gas at an elevated temperature in a heating zone which effects cracking of a substantial portion of said oil and producing oil and cracked products thru a production well therein, the improvement comprising pro viding in said heating zone during said cracking an injected hydrocarbon material comprising at least one aro matic-naphthenic compound readily dehydrogenatable under the conditions in said heating zone so as to depress coke formation.

7. The process of claim 6 wherein said hot gas is steam.

8. The process of claim 7 wherein said hydrocarbon material comprises principally Tetralin.

9. A process for recovering oil from an oil-bearing stratum penetrated by an injection well and a production well which comprises the steps of (l) injecting steam into said stratum thru said injection well to establish an oil-cracking zone at a temperature of at least about 600 F.;

(2) continuing the injection of steam so as to move said zone toward said production well and displace hydrocarbons thereinto;

(3) providing in said zone during cracking a hydrocarbon material comprising at least one aromaticnaphthenic compound which is readily dehydrogenatable under the cracking conditions therein, thereby suppressing coke formation normally elfected by said cracking; and

(4) recovering produced hydrocarbons from said production well.

10. The process of claim 9 wherein said hydrocarbon material is injected in vapor form with the injected steam.

References Cited UNITED STATES PATENTS 2,862,558 12/1958 Dixon 166-40 2,897,894 8/1959 Draper etal 166-9 3,093,191 6/1963 Glass 16611 3,263,750 8/1966 Hardy 166-11 

6. IN A PROCESS FOR RECOVERING OIL FROM AN OIL-BEARING STRATUM COMPRISING CONTACTING SAID OIL IN SAID STRATUM WITH A HOT GAS AT AN ELEVATED TEMPERATURE IN A HEATING ZONE WHICH EFFECTS CRACKING OF A SUBSTANTIAL PORTION OF SAID OIL AND PRODUCING OIL AND CRACKED PRODUCTS THRU A PRODUCTION WELL THEREIN, THE IMPROVEMENT COMPRISING PROVIDING IN SAID HEATING ZONE DURING SAID CRACKING AN IN JECTED HYDROCARBON MATERIAL COMPRISING AT LEAST ONE ARO MATIC-NAPHTHENIC COMPOUND READILY DEHYDROGENATABLE UNDER THE CONDITIONS IN SAID HEATING ZONE SO AS TO DEPRESS COKE FORMATION. 